Intensive human activities causing riverbed incision have increased the danger of compound flood in the PRD.

Estuary and coastal regions face the dual impacts of river flooding and storm surges, posing serious threats to the lives and properties of residents. The Guangdong-Hong Kong-Macao Greater Bay Area in China, an economically developed and densely populated region with a complex river network, is frequently affected by flood disasters. In recent years, rapid development in the Greater Bay Area, coupled with human activities such as sand mining and dredging, has significantly altered riverbed morphology, leading to a pronounced trend of incision. On one hand, riverbed incision increases the cross-sectional area, allowing for greater flood discharge; on the other hand, it changes the hydrodynamic conditions of the rivers, resulting in rising water levels in certain areas despite the incision.

This study employs a one-dimensional river hydrodynamic model and a storm surge model to simulate the impacts of river flooding and storm surges under various topographic conditions on flood disasters in the Greater Bay Area. The results indicate that the nonlinear interactions between floods and tides amplify the hazard of compound flooding in the mid-to-lower river network region. Furthermore, the severity of this hazard intensifies as the strength of flood-tide compound events increases.